Older CRX HF's are usually in worse shape and require a little bit more work. To make it a real gas mileage monster you'll need to swap out the engine and swap in a d15z1 engine. This includes the ECU, distributor, etc. This isn't totally needed toget you over 50mpg, but it will get you over 60mpg.
I'm trying to way out all my options, I can regularly buy 88-91 CRXs locally for under $2500, and even $900-1500 for some that need work.
With a little reseach I just realized that the CRX HF is geared for better fuel economy. If I do the engine swap, I assume I will not need that model, except for maybe some of the other HF Options (Like light wheels???)?
Without getting into engine swap details (I'm sure it is well documented on the internet), what advantage does the 92-95 Civic VX d15z1 engine have over the stock 88-91 CRX HF engine? (Let's say both are running at their peak efficency).
SVOBoy is right. The d15z1 (civic VX engine) has a unique design that actually can allow for air fuel ratios of 20:1. Below 3000 RPM one of the valves is only slightly open which actually causes a "swirling" action that helps promote leaner AFRs as well.
The d15z1 also has a 5-wire wideband oxygen sensor which can give better feedback and help achieve high AFR.
Oh, and it gets better power than the stock crx hf engine, so it won't seem so slow.
If you put a d15z1 engine into a civic/crx/etc made between 1988 and 1991 you'll need to get a transmission from a 1988-1991 car. (the 1988 is unique, the 1989-1991 are interchangeable)
I have a CRX HF transmission from a 1991 and will be mounting it to my d15z1 sometime soon. It will work in my 1989 civic sedan with no problems.
as far as I've been able to tell, the crx hf only came with steel rims, not sure what alloy of steel they used, but the steel rims from my crx hf are a few pounds lighter then the stock steel rims from my civic.
the popular answer you are going to get for rims is going to be civic vx, hx, or honda insight rims, there was also one modle of Miata rim that weighed around 12 pounds, and had the same bolt pattern, but I'm not sure about wheel offset.
If I had the time, and money ($3000 should defently be enough) and didn't need a back seat, and could find any crx's around here (there is maybe one for sale per month) I would get one, and swap a vx engine in to it, and just like the civic modles, the si is heaviest and base modle is lighter, and fuel effiecent modle is lightest.
one of the other things that both the crx hf and civic vx don't have that make them lighter, is a sway bar, and if you live in Nebraska or other windy states, you might notice that it's a little harder to handle in crose winds.